In a communications system, an encoding technology is generally used to improve reliability of data transmission and ensure quality of communication. A polar code (Polar code) is a first encoding and decoding algorithm that is theoretically proved to be capable of obtaining a Shannon capacity and has low encoding and decoding complexity (complexity of encoding and complexity of decoding are both O(NlogN)).
The polar code is a linear block code. An encoded code word of an original Polar code does not include an information bit, and the original Polar code is a non-system code. Because some communications technologies need to use a system code to perform encoding and decoding, application of the original Polar code in some communications technologies is limited.
In the prior art, a Gaussian elimination based method (Gaussian elimination based method) is used to transform the Polar code into the system code. However, after the Polar code is transformed into the system code in the prior art, complexity of the Polar code increases to O(N3), that is, the complexity of the Polar code is increased.